William Oughtred, a contemporary of Harriot, published an algebra, Clavis mathematicae, simultaneously with Harriot's treatise.

In 1712 he wrote two essays, which are still in manuscript, one on substance and accident, and the other called Clavis Philosophica.

His chief work appeared in 1713, under the title Clavis Universalis, or a New Inquiry after Truth, being a Demonstration of the NonExistence or Impossibility of an External World 1 (printed privately, Edinburgh, 1836, and reprinted in Metaphysical Tracts, 1837, edited by Sam.

The Clavis consists of two parts.

His Clavis Universalis is interesting on account of the resemblance between its views and those of Berkeley.

His biographer attributes the comparative failure of the Clavis to its inferiority in point of style, but the crudeness of his thought had quite as much to do with his failure to gain a hearing.

Historia do Futuro (Lisbon, 1718; 2nd ed., ibid., 1755); this and the Quinto Imperio and the Clavis Prophetarum seem to be in essence one and the same book in different redactions.

It seems certain that these conclusions were independent of Berkeley and Malebranche, and were not drawn from Arthur Collier's Clavis universalis (1713), with which they have much in common, but were suggested, in part at least, by Locke's doctrine of ideas, Newton's theory of colours, and Cudworth's Platonism, with all of which Edwards was early familiar.

- By consulting an account of my expenses at Cambridge, in the years 1663 and 1664, I find that in the year 1664 a little before Christmas, I, being then Senior Sophister, bought Schooten's Miscellanies and Cartes' Geometry (having read this Geometry and Oughtred's Clavis clean over half a year before), and borrowed Wallis's works, and by consequence made these annotations out of Schooten and Wallis, in winter between the years 1664 and 1665.

The last part, Hattatal, a treatise on metre, was written for Earl Skuli about 1222, in imitation of Earl Rognvald and Hall's Hattalykill (Clavis metrica) of 1150.